Ernest Christley wrote:
Ian Stirling wrote:

Best tool available to the amateur is a variable speed strobe - Party Light!

That way you can actually look and SEE what's happening.


That'll spot ordinary vibrations.
Torsional ones are a little bit harder.

Especially if you want, as you probably should, a graph of maximum stress
anywhere in the shaft/PSRU/Prop system vs RPM.

A few fine white lines down the length of the shaft will clear up that
problem.

Will they?
It'll obviously show huge torsional movement, but many, especially
shorter shafts may fail before it becomes visible.